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Commitca458ba

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Add PanicMessage type for PanicInfo::message().
1 parent8cd20cb commitca458ba

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3 files changed

+79
-11
lines changed

3 files changed

+79
-11
lines changed

‎core/src/panic.rs‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -12,6 +12,8 @@ use crate::any::Any;
1212
pubuseself::location::Location;
1313
#[stable(feature ="panic_hooks", since ="1.10.0")]
1414
pubuseself::panic_info::PanicInfo;
15+
#[unstable(feature ="panic_info_message", issue ="66745")]
16+
pubuseself::panic_info::PanicMessage;
1517
#[stable(feature ="catch_unwind", since ="1.9.0")]
1618
pubuseself::unwind_safe::{AssertUnwindSafe,RefUnwindSafe,UnwindSafe};
1719

‎core/src/panic/panic_info.rs‎

Lines changed: 69 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
usecrate::fmt;
1+
usecrate::fmt::{self,Display};
22
usecrate::panic::Location;
33

44
/// A struct providing information about a panic.
@@ -18,6 +18,17 @@ pub struct PanicInfo<'a> {
1818
force_no_backtrace:bool,
1919
}
2020

21+
/// A message that was given to the `panic!()` macro.
22+
///
23+
/// The [`Display`] implementation of this type will format the message with the arguments
24+
/// that were given to the `panic!()` macro.
25+
///
26+
/// See [`PanicInfo::message`].
27+
#[unstable(feature ="panic_info_message", issue ="66745")]
28+
pubstructPanicMessage<'a>{
29+
message: fmt::Arguments<'a>,
30+
}
31+
2132
impl<'a>PanicInfo<'a>{
2233
#[inline]
2334
pub(crate)fnnew(
@@ -29,12 +40,26 @@ impl<'a> PanicInfo<'a> {
2940
PanicInfo{ location, message, can_unwind, force_no_backtrace}
3041
}
3142

32-
/// The message that was given to the `panic!` macro,
33-
/// ready to be formatted with e.g. [`fmt::write`].
43+
/// The message that was given to the `panic!` macro.
44+
///
45+
/// # Example
46+
///
47+
/// The type returned by this method implements `Display`, so it can
48+
/// be passed directly to [`write!()`] and similar macros.
49+
///
50+
/// [`write!()`]: core::write
51+
///
52+
/// ```ignore (no_std)
53+
/// #[panic_handler]
54+
/// fn panic_handler(panic_info: &PanicInfo<'_>) -> ! {
55+
/// write!(DEBUG_OUTPUT, "panicked: {}", panic_info.message());
56+
/// loop {}
57+
/// }
58+
/// ```
3459
#[must_use]
3560
#[unstable(feature ="panic_info_message", issue ="66745")]
36-
pubfnmessage(&self) ->fmt::Arguments<'_>{
37-
self.message
61+
pubfnmessage(&self) ->PanicMessage<'_>{
62+
PanicMessage{message:self.message}
3863
}
3964

4065
/// Returns information about the location from which the panic originated,
@@ -116,7 +141,7 @@ impl<'a> PanicInfo<'a> {
116141
}
117142

118143
#[stable(feature ="panic_hook_display", since ="1.26.0")]
119-
implfmt::DisplayforPanicInfo<'_>{
144+
implDisplayforPanicInfo<'_>{
120145
fnfmt(&self,formatter:&mut fmt::Formatter<'_>) -> fmt::Result{
121146
formatter.write_str("panicked at ")?;
122147
self.location.fmt(formatter)?;
@@ -125,3 +150,41 @@ impl fmt::Display for PanicInfo<'_> {
125150
Ok(())
126151
}
127152
}
153+
154+
impl<'a>PanicMessage<'a>{
155+
/// Get the formatted message, if it has no arguments to be formatted at runtime.
156+
///
157+
/// This can be used to avoid allocations in some cases.
158+
///
159+
/// # Guarantees
160+
///
161+
/// For `panic!("just a literal")`, this function is guaranteed to
162+
/// return `Some("just a literal")`.
163+
///
164+
/// For most cases with placeholders, this function will return `None`.
165+
///
166+
/// See [`fmt::Arguments::as_str`] for details.
167+
#[unstable(feature ="panic_info_message", issue ="66745")]
168+
#[rustc_const_unstable(feature ="const_arguments_as_str", issue ="103900")]
169+
#[must_use]
170+
#[inline]
171+
pubconstfnas_str(&self) ->Option<&'staticstr>{
172+
self.message.as_str()
173+
}
174+
}
175+
176+
#[unstable(feature ="panic_info_message", issue ="66745")]
177+
implDisplayforPanicMessage<'_>{
178+
#[inline]
179+
fnfmt(&self,formatter:&mut fmt::Formatter<'_>) -> fmt::Result{
180+
formatter.write_fmt(self.message)
181+
}
182+
}
183+
184+
#[unstable(feature ="panic_info_message", issue ="66745")]
185+
impl fmt::DebugforPanicMessage<'_>{
186+
#[inline]
187+
fnfmt(&self,formatter:&mut fmt::Formatter<'_>) -> fmt::Result{
188+
formatter.write_fmt(self.message)
189+
}
190+
}

‎std/src/panicking.rs‎

Lines changed: 8 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -593,19 +593,18 @@ pub fn panicking() -> bool {
593593
#[panic_handler]
594594
pubfnbegin_panic_handler(info:&core::panic::PanicInfo<'_>) -> !{
595595
structFormatStringPayload<'a>{
596-
inner:&'afmt::Arguments<'a>,
596+
inner:&'acore::panic::PanicMessage<'a>,
597597
string:Option<String>,
598598
}
599599

600600
implFormatStringPayload<'_>{
601601
fnfill(&mutself) ->&mutString{
602-
usecrate::fmt::Write;
603-
604602
let inner =self.inner;
605603
// Lazily, the first time this gets called, run the actual string formatting.
606604
self.string.get_or_insert_with(||{
607605
letmut s =String::new();
608-
let _err = s.write_fmt(*inner);
606+
letmut fmt = fmt::Formatter::new(&mut s);
607+
let _err = fmt::Display::fmt(&inner,&mut fmt);
609608
s
610609
})
611610
}
@@ -627,7 +626,11 @@ pub fn begin_panic_handler(info: &core::panic::PanicInfo<'_>) -> ! {
627626

628627
impl fmt::DisplayforFormatStringPayload<'_>{
629628
fnfmt(&self,f:&mut fmt::Formatter<'_>) -> fmt::Result{
630-
ifletSome(s) =&self.string{ f.write_str(s)}else{ f.write_fmt(*self.inner)}
629+
ifletSome(s) =&self.string{
630+
f.write_str(s)
631+
}else{
632+
fmt::Display::fmt(&self.inner, f)
633+
}
631634
}
632635
}
633636

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